It is estimated that 30,000,000 Americans suffer from different types of iron related disorders, including a substantial proportion with profound iron deficiency syndrome. Detection of bioaccessible iron is one of the most important measurements that doctors can use for early detection if iron deficiency, iron overload or other types of immunological disorders.
To date iron is measured through a combination of blood tests that detect iron and iron binding capacity of transferrin, the protein that transports iron through the body. The current technology involves very sophisticated instrumentation which make this analysis prohibitively expensive and often requires qualified personnel to analyze the sample. Therefore, there is a need for the direct assay of iron that combines simplicity and economics. The present invention is directed to biosensors using transferrin, preferably lactoferrin, for detecting the amount of iron in a sample.
Although the technology relating to biosensors has been developing over the last 30 years, the specific application of transferrin for the detection of iron has not been disclosed. Various biocomponents (e.g. carbohydrates, amino acids, alcohols and certain proteins) are detected today with specifically designed potentiometric and amperometric electrodes. The original work on such electrodes was done by Clark Jr., L. C. and Lyons, C. published in Ann. N.Y. Acad. Sci. 102, p.29 (1962). In this first enzyme electrode, a glucose oxidase membrane was placed next to a platinum electrode to detect the products of the enzyme reaction in the presence of a substrate, glucose.
The characteristics of such electrodes are governed by the biorecognition of the analyte and the transport processes. In a recent edition of Biosensors: Fundamentals, Technologies and Applications, Edited by F. Scheller and R. D. Schmid, pp 129-132 (1991), a paper, "Biosensors for the Detection of Heavy Metal Ions and Fecal Contamination", discloses the use of phytochelatins, metallothioneins and polymerized glutathiones to complex and detect heavy metals. These materials however are not specific to iron or any other single heavy metal. In order to transduce the signal the authors, F. Binder et al, use a proton-sensitive field-effect transistor, generally referred to as an ion-selective field effect transistor (ISFET).
The ion-selective field effect transistor has been in development for many years. A chapter of the book Biosensor Technology, edited by Buck et al. and published by Marcel Decker, Inc., 1990, entitled "Solid State Potentiometric Sensors" by Jiri Janata, pp 17-34, reviews the development of such ISFET sensors. The specific work describes a sensor that incorporates the principle of the enzymatic reactions that result in the production of protons.
In an article "Unmediated amperometric enzyme electrodes" by George Wilson and Daniel Thevenot published in Biosensors, A Practical Approach Series, (edited by A. E. G. Cass and published by Oxford University Press), 1990, pp 1-17, discloses some techniques in producing electrodes. These electrodes are used in reactions which produce a small molecular weight electroactive species. Since these sensors can be used to monitor such a reaction without the need of a mediator, the sensor is called a "unmediated amperometric enzyme electrode".
A key development in later electrodes was the employment of membrane technology in order to eliminate the interference by substances other than the analyte electroactive substance. An excellent overview of biosensors in this regard, their development and application, is presented in Biosensors, edited by A. H. Hall and published by Prentice Hall, 1991.